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An auction system either live or timed runs by the clock. In a live auction, one often runs calls on a bid according to a clock. In a timed auction, you start and end an auction by a clock, and you show the users a countdown timer. The web page might show absolute times in the user time zone, but the local time has to be derived from the central clock. The presence of a central clock implies the need for a real-time web application to which the server sends updates.